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<br />TABLE 3
<br />
<br />HYDRAULIC S1'UDY REACIlES
<br />
<br /> (1) Downstream
<br /> Designation Descri"tion Control
<br /> , city shop, north of , , , trClcks slope-area
<br /> " C , , tracks eo Vine Prive critical depth
<br /> vine ''I
<br /> " Drive '0 Frey Avenue w,s, from U
<br /> N Frey '0 Lurimer .2 w.:S. from M
<br /> K Reuch , '0 Reach T w.:S. from N
<br /> T Reach K '0 Larimer " w.s. from K
<br /> , South of Vine Dr, Subdivision Slope-area
<br /> C Larior.cr #2 '0 Impala Oc, slope-areal
<br /> critical depth
<br /> I
<br /> , I ReilCh " '0 Laporte Ave. W.$, from D
<br /> Q Laporte '0 Reach R w,s, from C
<br />I R Faudre lIiryh SchOOl slope-area
<br /> ^ peudre High '0 Overland Tr<J.il "'lope-area
<br /> R I Qvorla,,::! TTail '!'railer Park w,s, from "
<br />I
<br /> , Larimer " through Irish Green slope-areal
<br /> critical depth
<br /> , IriSh Gre.'n '0 Hollywood Ave, w.s, from ,W""
<br />
<br />(l}:;oc Ro.-,.ch ;.QccJ.tion ",;1<,
<br />
<br />(2)waLer s,-,r(act'
<br />
<br />Gp tlTe! usn
<br />, HYDRAULIC STUDY REACHES 3
<br />
<br />-;;8-
<br />
<br />downstream starting water surface elevation (for sllbcri tical
<br />flow) and cross section data. Peak discharges l1re discClssed
<br />in the hydrology section of this report,
<br />
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<br />
<br />A field survey, co~plete with photographic documentation,
<br />W<ilS completed to determine Ma.nning's 'n' values, At the time
<br />of this investigation the majority of vegetation was in full
<br />foilage. During computation every effort was made to correlate
<br />the values with those of similar conditions in photographs
<br />originally published by the U.S. Department of Agriculture
<br />and reproduced by Chow!61 In some cases. 'n' values were
<br />calculated using procedures outlined by Chow. A photo
<br />catalo~76f channel reaches and representative '0' values was
<br />submitted to the Technical Committee for review on October 30,1980,
<br />l1nd is on file with the City of Fort Collins.
<br />
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<br />,
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<br />,
<br />,
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<br />
<br />The standard step method used in HEC-2 is such that dn error
<br />in starting water surface elevation is corrected as the program
<br />proceeds upstream, Nevertheless an incorrect startin~ point
<br />can c<iluse significant changes in the floodplain of the lower
<br />r'eaches, Several mfCthods were used to determine the startinq
<br />water surface elevati.ons (Tablo ,\, On n'ac-h",t" wh<'r+" th",
<br />ulschar~~ ov~r-to~pcd d road Or railwJY the critical depth was
<br />computed and used ilt" a starti.ng elevation, Reaches U & Mare
<br />examples. OthHr reaches st~rt at natural detention an!a.';
<br />(reaches I & D), For these reaches a starting elevation was
<br />calculated from the stage-storage relationship modelled in thp
<br />S.W.M,M, program. ~any reaches had their most downstream
<br />Cyoss-section In common with the upstream cross-sectio~ of a
<br />lower reach, In these CilS".'; the water surface elevation
<br />calculated for the lower reach was used as input to the upper
<br />reach. This is by far the most accurute procedure. Fir-ally,
<br />flow nplits '>t the Poudre liigh Scr.ool made it neceS5ary to
<br />establish intermediate water surface elevations, ?hc Slope area
<br />method was us<.'d to corr.<,ute a contrOl ".-at.~r surface. 1'his
<br />special case lS discussed 1'1 4reater detail in paragraphs t.e
<br />follOW.
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<br />-29-
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